Ozone is a strong oxidizing agent. It has many uses in sanitation and sterilization: as a germicide, bactericide, or a general antiseptic. One particular use of ozone, or ozonated air, is in the purification of waste and wastewater, especially in the secondary or tertiary treatment of sewage, or oxidation of industrial waste either liquid or gaseous. It is also used in various processing steps in the manufacturing sector.
In the context of sterilization or sanitation, ozone has a number of desirable characteristics. First, it is, relative to other sanitation and sterilization agents, environmentally safe. Although it is caustic, requiring certain safeguards in storage, handling and use, ozone occurs naturally through a variety of chemical pathways. Its degradation product is elemental oxygen. Ozone is a gas at room temperature and is handled easily, without many of the hazardous material handling requirements associated with alcohols and/or volatile hydrocarbons.
There are several known methods for producing ozone from air or another oxygen-containing gas. A number of the known commercially used processes for making ozone employ an electrical discharge. Oxygen, or a gas containing molecular oxygen typically air is passed between two electrodes separated by a dielectric material. The electrical discharge converts a portion of the gas to ozone and an ozone enriched gas is drawn off from the area through which the current passes.
Typically, the types of apparatus which have been used to produce ozone have two electrodes, separated by a dielectric barrier, and a space for the fast flow of a gas containing molecular oxygen. The gas flows through the region between the electrodes, through which a high electrical discharge passes. Different arrangements of these elements are known. A common arrangement is for the two electrodes to be in the shape of concentric tubes. In this configuration, the feed gas flows through the annular gap between the two tubes. The electrodes are separated by a dielectric material, usually glass. The outer tube can be made of stainless steel while the inner electrode may comprise a thin metal layer deposited on the inside of the dielectric glass tube. Typically, a commercial ozone generator will comprise a number of these electrode pairs, in order to produce a sufficient quantity of ozone for the desired purpose.
In various of the known methods for producing ozone, prior to the present invention, the process described above is limited by low efficiencies of conversion of the gas containing oxygen into ozone, relative to the amount of electrical energy input into the apparatus. Known apparatus transfer a substantial portion of their input electrical energy into heat, raising the temperature of the apparatus as well as that of the discharged gas. Thus, they typically require cooling systems.
Cooling systems for ozone generating equipment are typically expensive, comprising a substantial portion of the total capital cost of the apparatus. In addition, cooling systems require further energy input, further reducing the energy efficiency of the conversion of feed gas into ozone. Moreover, cooling equipment imposes additional maintenance requirements on the operation of the ozone generating unit. The cooling system must be operational in order for the system to deliver ozone at a usable temperature in many applications. For example, the air discharge temperature of existing units can reach 300.degree. C., when the cooling system fails. In addition to these problems, the known apparatus for producing ozone typically have only one dielectric barrier. The remaining electrode, therefore, is subject to degradation by the ozone produced in the apparatus.
The relatively low energy efficiency of existing apparatus for producing ozone leads to the consumption of large amounts of electricity to produce ozone using apparatus prior to the present invention. This imposes additional environmental burdens.
When considering the inputs necessary to produce ozone, it is important to consider the additional burdens imposed by the production of the electrical energy used in the relatively inefficient known processes for producing ozone. The cost of producing even low concentrations of ozone is extremely high, relative to the competing means for sanitizing and sterilizing. The high cost of producing ozone tends to discourage large commercial and industrial use of ozone as a sterilizing or sanitizing agent, and in particular, in the purification of water or wastewater.
Accordingly, there is a need for a low cost, energy efficient ozone generator that is simple, compact, and economical. Moreover, such an apparatus must be reliable, inexpensive, and easy to use and maintain. Prior approaches do not adequately address the problem of providing such an ozone generator. It is, therefore, desirable to produce an efficient means of making ozone that does not require cooling systems, and in which the discharge temperature of the air has been raised only minimally.